1. Field
An embodiment of the present invention relates to a surface position detecting apparatus which detects surface position information of a predetermined surface in an object, an exposure apparatus incorporating this surface position detecting apparatus, a device manufacturing method for manufacturing such micro devices (electronic devices) as semiconductor devices or liquid-crystal display devices, using the exposure apparatus, and a surface position detecting method.
2. Description of the Related Art
A lithography process for manufacture of the semiconductor devices and others is carried out using an exposure apparatus for transferring a pattern formed on a reticle (mask), onto a wafer (or a glass plate or the like) having a surface coated with a resist (photosensitive material), through a projection optical system. The exposure apparatus in use is, for example, a reduction projection exposure apparatus of the step-and-repeat method (so called a stepper), or a scanning projection exposure apparatus of the step-and-scan method of synchronously scanning the reticle and the wafer (so called a scanning stepper).
As the semiconductor devices increase their integration degree and pattern fineness, the exposure apparatus is required to transfer the pattern in a high resolving power (high resolution). For this reason, in order to prevent image blurring or the like due to defocus, the exposure apparatus needs to perform exposure while keeping a wafer surface within a range of the depth of focus (DOF) of the image plane of the projection optical system (the best focus plane of the pattern). Therefore, the exposure apparatus is equipped with an autofocus sensor (hereinafter referred to as an AF sensor) to measure the position of the wafer surface (surface position) in the direction of the optical axis of the projection optical system, and is configured to control the height and inclination angle of a wafer stage on the basis of a measured value by this AF sensor.
The conventional AF sensor for the wafer surface is constructed with a sensor of an oblique incidence method configured to project a slit image or the like from an oblique direction to the wafer surface, measure a position of a position of the slit image or the like formed by light reflected on the wafer surface, and obtain the surface position information on the basis of the principle of triangulation from the measurement result (e.g., cf. U.S. Pat. No. 5,633,721).